Case Presentation: A 91 year-old female with history of atrial fibrillation on coumadin, hypertension, prior stroke, myeloproliferative disease, polycythemia vera and recently diagnosed macular degeneration presented with complaints of visual hallucinations for two weeks. She was in her usual state of health when she developed sudden onset of vivid visual hallucinations including people coming in her house, rummaging through her things looking for her paperwork, dogs running around the house, and a river running through her house. Other than insomnia her review of systems was negative. She denied headache or cognitive decline. She was seen by her PCP and treated for a presumed urinary tract infection without resolution of her symptoms. She was then sent to the ER and admitted for evaluation of her altered mental status. Her physical exam revealed an alert, fully oriented elderly female with stable left facial droop, decreased right eye visual acuity without any new neurological deficits, a normal mini mental exam and no signs of Parkinsonism. Vital signs were stable and labs revealed baseline leukocytosis and thrombocytosis. Urinalysis was negative. Brain MRI revealed chronic micro-vascular changes and stable known chronic infarct and a spot EEG was negative for seizures or epileptiform activity. Medication list review revealed no obvious culprits. Her intermittent visual hallucinations persisted while inpatient. Given her negative medical and neurological work up and recent development of macular degeneration, her altered mental status was most consistent with Charles Bonnet Syndrome (CBS).

Discussion: Altered mental status, hallucinations, and behavior changes are commonly heard complaints by internists, especially in the elderly. Often these are explained by delirium and/or dementia, but when patients present, as ours did, with isolated visual hallucinations, the differential needs to be broadened. CBS is a poorly understood phenomenon that produces hallucinations in 12% of visually impaired patients without underlying psychiatric or neurological conditions. Rates are higher in patients with macular disease and directly corresponds to the degree of visual impairment: the higher level of visual impairment, the more commonly it occurs. Living alone appears to further increase the risk. It is characterized by vivid and complex visual hallucinations that are known to the patient not to be real. The cause is unclear, but fMRIs of patients experiencing these hallucinations show increased activity in the ventral occipital lobe, suggesting cortical hyper-excitability “creates” these hallucinations, similar to a phantom limb syndrome. Currently there are no validated treatments, however some patients find relief with behavior modifications such as improved lighting, blinking, and engaging the hallucinations. Anecdotally, severely persistent and distressing cases can trialed on anti-psychotics, anti-cholinesterase inhibitors, SSRIs or anti-seizure drugs.

Conclusions: Charles Bonnet Syndrome (CBS) should be included in the differential diagnosis in patients presenting with altered mental status. Visual hallucinations in the setting of macular degeneration and older age are most consistent with CBS. It is often under recognized and frequently misdiagnosed as psychosis, delirium or dementia. It is a benign condition that usually does not require pharmaceutical treatment therefore proper diagnosis can prevent unnecessary medication and provide proper reassurance to patients and families.